Radiation images such as X-ray images have been widely used for diagnoses of medical conditions in medical sites. In recent years, a radiation imaging system equipped with a radiation detector has become popular. This system acquires two-dimensional image data through radiation as an electrical signal by the radiation detector, and processes this signal to be displayed on a monitor.
A scintillator panel plays a role in converting incident radiation from the substrate side to light. A flat panel detector (FPD) developed in the 1990s as an imaging device for radiation images is a radiation detector combined with a scintillator and an imaging device. As a material for this scintillator, cesium iodide (CsI) is commonly used. The reason of it is to suppress scattering of emission light because of optical guide effect, since CsI exhibits a high X-ray-to-visible light conversion efficiency, whereby a columnar crystal structure can be easily formed via vacuum evaporation (refer to Patent Document 1, for example).
As a method of preparing such the radiation detector, commonly known is a method of forming CsI directly on an imaging device via vacuum evaporation (refer to Patent Documents 2 and 3, for example). There is another possible method in which a scintillator panel adheres to an imaging device (refer to Patent Document 4, for example).
However, in each case, designing of a phosphor layer to transmit a light signal converted by a scintillator efficiently has not been tested.
(Patent Document 1) Japanese Patent O.P.I. Publication No. 5-93780
(Patent Document 2) Japanese Patent O.P.I. Publication No. 5-312961
(Patent Document 3) Japanese Patent O.P.I. Publication No. 6-331749
(Patent Document 4) Japanese Patent O.P.I. Publication No. 2003-66196